Ubiquitous network access has been almost realized today. From network infrastructure point of view, different networks belong to different layers (e.g., distribution layer, cellular layer, hot spot layer, personal network layer, and fixed/wired layer) that provide different levels of coverage and connectivity to users. Because the coverage of a specific network may not be available everywhere, and because different networks may be optimized for different services, it is thus desirable that user devices support multiple radio access networks on the same device platform. As the demand for wireless communication continues to increase, wireless communication devices such as cellular telephones, personal digital assistants (PDAs), smart handheld devices, laptop computers, tablet computers, etc., are increasingly being equipped with multiple radio transceivers. A multiple radio terminal (MRT) may simultaneously include a Long-Term Evolution (LTE) or LTE-Advanced (LTE-A) radio, a Wireless Local Area Network (WLAN, e.g., WiFi) access radio, a Bluetooth (BT) radio, and a Global Navigation Satellite System (GNSS) radio. In the MRT, the LTE-A radio is an Orthogonal Frequency Division Multiple Access-based (OFDMA-based) mobile broadband technology that is capable of providing global roaming services, and the WiFi radio is capable of providing huge bandwidth transmission via local access. The combination of LTE-A and WiFi radio is one of the examples of WiFi offloading, which is a common paradigm of future communications. Multiple radios co-located or coexisted in the same communication device are also referred to as in-device coexistence (IDC).
Due to spectrum regulation, different technologies may operate in overlapping or adjacent radio spectrums. For example, LTE/LTE-A TDD mode often operates at 2.3-2.4 GHz, WiFi often operates at 2.400-2.483.5 GHz, and BT often operates at 2.402-2.480 GHz. Simultaneous operation of multiple radios co-located/coexisted on the same physical device, therefore, can suffer significant degradation including significant coexistence interference (e.g., IDC interference) between them because of the overlapping or adjacent radio spectrums. Due to physical proximity and radio power leakage, when the transmission of data for a first radio transceiver overlaps with the reception of data for a second radio transceiver in time domain, the second radio transceiver reception can suffer due to interference from the transmission of the first radio transceiver. Likewise, data transmission of the second radio transceiver can interfere with data reception of the first radio transceiver.
Various IDC interference mitigation solutions have been sought. Among the different interference mitigation solutions, power management is one of the possible solutions. One fundamental problem for IDC interference is that the transmission power of one radio transceiver is too strong to allow simultaneous reception on another co-located/coexisted radio transceiver. Therefore, if the transmitting radio transceiver can reduce its transmission power, then simultaneous reception of other transceivers becomes possible. In general, power control (PC) is a common functionally supported by every radio transceiver so reusing such mechanism to mitigate IDC interference is a low cost and backward compatible option. Power control can be used as a lightweight solution before applying other heavyweight solutions that either require more resource or control overhead (e.g., FDM/RRM), or have higher impact on throughput (e.g., TDM).
In LTE/LTE-A systems, most of the activities of a mobile station (UE) are controlled by the network and the serving base station (eNodeB). For example, the transmit power of each UE needs to be maintained at a certain level and regulated by the network in OFDMA systems. The maximum UE output power and the current UE transmit power, however, is different depending on UE capability and usage. Typically, an eNodeB adjusts the transmit power of each UE based on the following information from each UE: power headroom report (PHR), UE-configured maximum transmitting power (Pcmax), sounding reference signal (SRS), and channel quality indicator (CQI). On the other hand, each UE adjusts its own transmitting power based on the pathloss compensation (open loop PC) and based on physical downlink control channel (PDCCH) grant or transmit power control (TPC) command (close loop PC) from the serving eNodeB. To mitigate IDC interference via power control, it is desirable for the UE to indicate the IDC interference problem such that the serving eNodeB can adjust the transmitting power of the UE accordingly.